Many chemical polymerization processes are conducted in the presence of water or other fluids and the polymer or resin produced is suspended in the fluid. These processes are referred to as suspension processes. Other processes in which particle sizes are reduced by grinding in the presence of water or other fluids also produce suspensions of solid particles in a fluid. In both of these types of suspension processes, there are produced some oversized particles, or agglomerations of particles, which are larger than desired and which must be separated and removed. When a suspension or a slurry (a suspension of solid particles in a liquid) is passed over a relatively coarse filter medium such that the oversized particles or agglomerations of particles are retained by the filter medium while the remainder passes through with the fluid in the form of a suspension, the filtration process is known as wet screening. Wet screening, or separation of these oversize particles, or agglomerates of particles, has been accomplished heretofore by various means. One device commonly used in the PVC industry is a vibrating wet screen separator. This type of device contains a horizontal circular or rectangular screen which can be up to 6 feet in diameter, or of a larger rectangular area, contained within a housing. The screen is vibrated at a high frequency by an electric motor-mounted eccentric weight. The slurry is fed through a port in the top of the housing and onto the screener; acceptably sized PVC particles and water pass through the screen, or filtering medium, while oversize and agglomerated particles are retained on the upper surface of the screen and are moved by the vibrating action to its periphery where they are withdrawn from the side of the housing. All piping connections to and from this screener must be made with flexible connections to accommodate the vibration. In addition, the device can only be mounted with the screen in a horizontal, or nearly horizontal, position and so that the slurry is admitted at the top and withdrawn from the bottom of the housing. In addition to being relatively expensive to purchase and operate, this type of prior art screening device has three deficiencies: periodic failure of the flexible connections can result in substantial emissions of VCM to the atmosphere; the metal body and housing of the screener are subject to fatigue failure which results in VCM emissions; and, due to the light construction required to allow vibration, the screener bodies are incapable of withstanding fluid pressures of greater than about 1 psig.
Other prior art devices, such as box and cone filters, require elaborate procedures to prepare the device for clean-out so as to reduce VCM levels. Washing or manual removal of the screen or other filter medium, an unpleasant and often hazardous task, is required to remove separated and entrapped oversize or agglomerated particles.